The invention relates to a magnetic disk unit, and particularly relates to a magnetic disk unit having two types of actuators, that is, coarse actuators for large movement and micro actuators and further having a controlling IC on a suspension supporting a magnetic head.
As a prior art of the invention, JP-A-11-195215 discloses that, in a magnetic head-supporting mechanism having two-stage actuators and an IC (integrated circuit) mounted in a suspension, the mechanism is provided with means for preventing the IC itself from being damaged due to heat occurring during the operation of the IC. Further, regarding a conventional head-supporting mechanism of one stage, JP-A-4-103085 discloses a controlling method for compensating the position deviation of the head-supporting mechanism which deviation occurs due to temperature rise of a magnetic disk unit.
In a chip-on-suspension (hereinafter referred to as COS) in which an IC is mounted on a suspension, there is such a case as a magnetic head deviates in the direction of the radius of a disk due to the temperature rise of the IC.
In a magnetic disk unit having a plurality of magnetic heads mounted therein, there is such a case as, in a plurality of magnetic heads initially located in an identical cylinder, a certain magnetic head successively performs reading or writing, and in this case there occurs a phenomenon explained below. In the case where one magnetic head is successively operated, the IC of the magnetic head rises, so that a suspension is deformed with the result that the successively operated magnetic head and other magnetic heads (non-operated magnetic heads) deviate in the direction of the radius. The successively operated magnetic head is servo-controlled to thereby follow the identical cylinder. In this state, when magnetic-head-switching from the successively operated magnetic head to another magnetic head is performed, the magnetic head commencing the operation by the magnetic-head-switching comes to lose its location because the switched magnetic head is located in another cylinder different from that of the successively operated magnetic head. Thus, it is necessary for the switched magnetic head to seek in the direction of the radius so that location information recorded in a disk may be read out. Accordingly, since it is impossible to immediately perform the writing/reading of data, there is such a problem as the transfer speed decreases.
Further, in a case of writing servo information (location information) through STW (servo track writer), there is such another problem as tracks can not be written at an equal pitch due to the thermal deformation.
The object of the invention is to obtain a magnetic disk unit having a plurality of suspensions in the same cylinder, in which magnetic disk unit, even at a time when reading/writing operation is transferred from the first suspension to the second suspension under a state that servo control is performed regarding the first suspension while a heating element such as IC is operated in the first suspension, it is possible for the transferred, second suspension to perform smooth operation.
According to the first aspect of the invention, there is provided a magnetic disk unit having micro actuators for slight movement and an IC for amplifying the reading/writing signals of a magnetic head which IC is mounted on a suspension, the magnetic disk unit comprising: a sensor for monitoring the temperature of the IC which is operating (, that is, during the reading/writing operation of the magnetic head); and means for compensating the location of the magnetic head of a suspension mounting the IC the temperature of which rises, in compliance with the temperature variation (temperature rise) by use of the micro actuators. In other words, the amount of displacement which occurs regarding the magnetic head due to the temperature rise of the IC is compensated by the micro actuators. This compensation is performed by a displacement amount corresponding to the temperature rise while sensing the temperature rise of the IC through the sensor. In this case, it is necessary to previously measure a relation between the temperature rise and the displacement amount, and by use of a table in which this relation is written, the compensation can be performed. Alternatively, the compensation table of the magnetic head relating to the temperature rise of the IC (, that is, the relation between the compensation amount of displacement of the magnetic head and the temperature rise) may be previously stored in the IC.
Further, in a case of successively writing information as in the case of the STW, the IC may be preheated prior to the writing of the information up to a temperature corresponding to that of the successive writing, and the preheating is ceased at the same time as the writing is commenced. By these, since the temperature of the IC is kept to be constant, it becomes possible to prevent the thermal displacement of the magnetic head from occurring due to the temperature rise caused with the elapse of time after the commencement of the writing, whereby it is possible to write servo information at an even track pitch. (Further, by keeping the temperature of the IC so that it may be the temperature of the successive writing or successive reading, the amount of the thermal displacement of the magnetic head can be kept to be constant. Thus, it becomes possible to prevent the thermal displacement of the magnetic head from occurring due to the temperature rise caused after the commencement of the writing or reading.)
Further, by providing controlling means for maintaining a predetermined temperature regarding the IC while detecting the temperature of the IC, it becomes possible to record servo information at an even track pitch from the inner periphery of a disk to the outer periphery thereof. Since the flow rate of air flow above the inner periphery of the disk differs from that above the outer periphery thereof, the temperature of the IC varies in a case of heating with the same amount of heat generation insofar as the inner and outer peripheries are concerned, so that there occur such a problem as no writing can be performed at an even track pitch. However, by providing the controlling means for making the IC temperature constant, the thermal displacement becomes constant between the inner and outer peripheries of the disk, whereby the servo information can be recorded at the even track pitch. Thus, the precision of positioning and the quality of reading/writing are enhanced, so that high recording density can be achieved.